Ronnie O'Sullivan gave Matthew Stevens a flicker of hope in their World Championship semi-final before trampling over his Welsh opponents' hopes with a devastating six-frame burst.

O'Sullivan has never lost a Crucible final and barring a spectacular turnaround on Saturday he is heading to the fourth of his career. Given the way he finished against Stevens on Friday, there is now every prospect of the 36-year-old triumphing with a session to spare, having already built an 11-5 lead in the best-of-33-frame contest.

He ran in breaks of 61, 62, 110, 98, 90 and 113, clicking into the form that has taken him past three former world champions in Sheffield. Peter Ebdon, Mark Williams and Neil Robertson had no answer to O'Sullivan's brilliance in the earlier rounds and, although Stevens was briefly level, having started 5-3 in arrears, trouble soon began to mount for the Carmarthen player as O'Sullivan found an almost unstoppable momentum.

It was not that Stevens was off-guard. He knew the danger lurked, but when it arrived there was no stopping O'Sullivan. He is hungry this year, and whatever he says to contradict that needs to be taken with a large pinch of salt.

Another Welshman, Mark Williams, was on the receiving end last Sunday when O'Sullivan hit him with a six-frame assault. As Stevens admitted: "On the form he showed in that second session against Mark Williams, no one can beat him. "But every day is different so if I play my game I've hopefully got half a chance."

The two-time runner-up, came out playing purposefully and a run to 60 gave him the opening frame, before he raised the bar with a terrific clearance of 63 in the next, after O'Sullivan had led 62-0. Showing composure under intense pressure, he cut in a difficult pink to the middle before firing in the black to take the frame by a single point.

It was just the start Stevens was hoping for but his fortunes then rapidly changed. A 62 break from O'Sullivan restored the three-time champion's lead and, when Stevens played a poor safety in the next frame, striking the wrong red, in went the first century break.

The punishment was then relentless. Left a long red, O'Sullivan, already 29-4 ahead, drilled it in and cleared the table. When Stevens played a swerve but missed a red over a top pocket by millimetres, the chance was devoured and another century almost followed, O'Sullivan missing a red on 90.

It took several efforts to bring up the 10-5 lead but only one to add another frame, the eighth century of O'Sullivan's championship underlining the tall order facing Stevens. Wales' last remaining player in the competition needs an aberration of a session from the man least likely to provide one.

Ali Carter was considering retirement at the turn of the year but now a second appearance in the World Championship final beckons for the 32-year-old from Tiptree. He leads Stephen Maguire 14-10 overnight after dominating a large part of their two sessions on Friday.

The final three frames of the day went Maguire's way, though, as he belatedly found some mental poise, but the Scot still faces a tall order when they play to a finish tomorrow afternoon.